Water running is an excellent form of cross training, as well as a good way to maintain fitness while recovering from a running injury. Running in the deep end of a pool (while wearing a flotation belt) helps build strength and stamina just as running on land, but with no impact to your legs. Many runners and tri-athletes find their way to this form of exercise after an injury, but if you're healthy, replacing an easy run day with a pool running workout will help you stay that way. It looks weird, it feels weird, but it's a deceptively hard workout. With an Aqua jogger strapped around your waist, climb into the deep end of the pool. Move your arms the same as if you were running normally. Keep your body straight, and don't let your butt stick out. Don't point your toes, or you might end up with nasty foot cramps. Breathe. Focus on intensity rather than stride rate, because your stride rate will be slower in the water due to the increased resistance. When you do this, you will likely notice that you don't go anywhere. That's normal, and another reason it seems weird: I'm running, but I'm not going anywhere! Because the scenery doesn't change much, pool running can feel monotonous if you're alone. Consider dragging a training partner along, or look into the water running classes at the YMCA, JCCSF, or elsewhere. The YMCA's Presidio branch offers a class two nights a week and Saturday morning, led by physical therapists from Presidio Sports and Medicine. I've taken these classes before and really enjoyed them, although admittedly I would have much rather been on dry ground! You'll find a mix of broken athletes, water aerobics buffs, and people who just want a challenging workout in the water. Bonus: You can soak in the hot tub afterwards!